Peel the 1 large sweet onion and cut it into slices about 1/2 inch thick. Carefully separate the onion into individual petals, use a sharp knife to cut into pieces.
In a bowl, whisk together 1 cup all-purpose flour, 1/2 cup cornstarch, 1 tsp baking powder, 1 tsp garlic powder, 1/2 tsp paprika, and Salt and pepper.
In a separate bowl, beat the 2 large eggs and 1 cup buttermilk together.
Dip each onion petal into the flour mixture, then the egg mixture, and coat again in the flour mixture. Finally, coat in 1 cup breadcrumbs.
Preheat the air fryer to 375°F (190°C).
Arrange the coated onion petals in a single layer in the air fryer basket. Lightly spray with Olive oil spray.
Air fry for 10-15 minutes, flipping halfway through, until golden brown and crispy.
In a small bowl, mix 1/2 cup ranch dressing,1 tbsp ketchup 1 tbsp horseradish (if using), and 1/2 tsp garlic powder. Adjust to taste.
Once the Texas Tonion is crispy and golden, serve with the dipping sauce on the side.